Solar Panels 400ft From House....19360 KW system with 3 SMA SB 7.0-US inverters

Dan_C Registered Users Posts: 2
I'm trying to figure out how to get the power from my panels back to my house, with acceptable Voltage drop.

I'm wondering if I can run DC back to house with  3 x 2 Pairs of 4 AWG aluminum then hook to inverters, or should I have a breaker box and inverters out with solar panels and run the AC back on 350mm wire?......Thanks for the help in advance....Dan


  • animatt
    animatt Solar Expert Posts: 295 ✭✭✭
    edited November 2016 #2
    Your dc runs could be much higher voltage. 
    Each of your 3 arrays would be connected to roughly 6500w.
    Run that at something like 450v.  Would leave you with about 14.5 amps to move at peak power.(per array)

    A pair of 10awg gauge copper wire could do that.

    At ac transmission you would be transmitting at 240v
    That is 80 amps at peak.  1/0 should handle that approximately 100kmils

    Price your options.  Will you ever need or want ac power out by the array? If so transmitting via ac maybe benificial. 
  • Dan_C
    Dan_C Registered Users Posts: 2
    Thanks for helping me on this.

    So, I was trying to stay with alumninum for the 400ft long, and in order to maintain 3% Voltage drop or less, the tools were saying I needed like #250 aluminum or like 4/0 copper (which looks really expensive).

    Is the 3% voltage drop the real target (as all the tools seem to say so) or can I go higher?

    Here is output of the voltage drop tool..


    1 conductors per phase utilizing a #250 Aluminum conductor will limit the voltage drop to 2.64% or less when supplying 80.0 amps for 400 feet on a 240 volt system.
    For Engineering Information Only:
    205.0 Amps Rated ampacity of selected conductor
    0.09 Ohms Resistance (Ohms per 1000 feet)
    0.041 Ohms Reactance (Ohms per 1000 feet)
    7.199999999999999 volts maximum allowable voltage drop at 3%
    6.328. Actual voltage drop loss at 2.64% for the circuit
    0.9 Power Factor

  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    For long runs, it makes economic sense to use higher voltage drops than for short runs.

    I am available for custom hardware/firmware development

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    AFAIK the 3% was established based on the (old) High cost of PV panels say 10 or more years ago.... So now with cheap PV prices, you need to do a calculation to see what the cost of losing 3% is vs the cost of adding another  cheaper PV to send more watts to the inverter(s)....
    Agree with all comments about  sending higher DC current.
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  • animatt
    animatt Solar Expert Posts: 295 ✭✭✭
    I get 1 awg copper would get you a 3.3% drop at 80 amps 240v
    But a more realistic 65 amps 2awg copper gives a 3.39% drop

    2/0 awg aluminum gives a drop of 3.28% at 80amps 240v

    These are much smaller than what you thought you may need.  But I am cheap and even 2awg is expensive to me.
    3 pairs of 10awg cabling would do your 3 arrays. 

    So calculate rate of 1200ft [400x3]  2 conductors. 10awg.
    400ft of 2

    Only reason I see to do ac transmission is if you need ac power out that way anyway.
    I am going to do an array at a similiar distance yours is.  Mine will do ac transmission because I need power out there anyway.

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    I would lean toward HV DC transmission, and if you need AC out there, drop in some 1/2 PVC and pull AC back out to there while you have a trench open.   I think AC & DC can go in the same trench, but not in the same conduit.
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